Three-dimensional (3d) printing

ABSTRACT

In a three-dimensional printing method example, a polymeric or polymeric composite build material is applied. A fusing agent is applied on at least a portion of the build material. The fusing agent includes an aqueous or non-aqueous vehicle and an inorganic pigment dispersed in the aqueous or non-aqueous vehicle, wherein the inorganic pigment is selected from the group consisting of lanthanum hexaboride, tungsten bronzes, indium tin oxide, aluminum zinc oxide, ruthenium oxide, silver, gold, platinum, iron pyroxenes, modified iron phosphates (A x Fe y PO 4 ), modified copper pyrophosphates (A x Cu y P 2 O 7 ), and combinations thereof. The build material is exposed to electromagnetic radiation, thereby fusing the portion of the build material in contact with the fusing agent to form a layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S.application Ser. No. 15/763,223, filed Mar. 26, 2018, which itself is anational stage entry under 35 U.S.C. § 371 of PCT/US2015/057185, filedOct. 23, 2015, each of which is incorporated by reference herein in itsentirety.

BACKGROUND

Three-dimensional (3D) printing may be an additive printing process usedto make three-dimensional solid parts from a digital model. 3D printingis often used in rapid product prototyping, mold generation, and moldmaster generation. Some 3D printing techniques are considered additiveprocesses because they involve the application of successive layers ofmaterial. This is unlike traditional machining processes, which oftenrely upon the removal of material to create the final part. Materialsused in 3D printing often require curing or fusing, which for somematerials may be accomplished using heat-assisted extrusion orsintering, and for other materials may be accomplished using digitallight projection technology.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference numerals correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference numerals orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1 is a flow diagram illustrating an example of a 3D printing methoddisclosed herein;

FIG. 2 is a simplified isometric view of an example of a 3D printingsystem disclosed herein;

FIG. 3 is a photographic image of 3D printed parts formed by an exampleof the 3D printing method disclosed herein; and

FIG. 4 is a photographic image of other 3D printed parts formed byanother example of the 3D printing method disclosed herein.

DETAILED DESCRIPTION

Examples of the three-dimensional (3D) printing method and the 3Dprinting system disclosed herein utilize Multi Jet Fusion (MJP). Duringmulti jet fusion, an entire layer of a build material (also referred toas build material particles) is exposed to radiation, but a selectedregion (in some instances less than the entire layer) of the buildmaterial is fused and hardened to become a layer of a 3D part. In theexamples disclosed herein, a fusing agent is selectively deposited incontact with the selected region of the build material. The fusingagent(s) is capable of penetrating into the layer of the build materialand spreading onto the exterior surface of the build material. Thisfusing agent is capable of absorbing radiation and converting theabsorbed radiation to thermal energy, which in turn melts or sinters thebuild material that is in contact with the fusing agent. This causes thebuild material to fuse, bind, cure, etc. to form the layer of the 3Dpart.

Fusing agents used in multi jet fusion tend to have significantabsorption (e.g., 80%) in the visible region (400 nm-780 nm). Thisabsorption results in strongly colored, e.g., black, or stronglycolored, 3D parts. Examples of the method and system disclosed hereinutilize a fusing agent containing a plasmonic resonance absorberdispersed in an aqueous or non-aqueous vehicle. The fusing agent,containing the plasmonic resonance absorber, has absorption atwavelengths ranging from 800 nm to 4000 nm and transparency atwavelengths ranging from 400 nm to 780 nm. As used herein “absorption”means that at least 80% of radiation having wavelengths ranging from 800nm to 4000 nm is absorbed. As used herein “transparency” means that 20%or less of radiation having wavelengths ranging from 400 nm to 780 nm isabsorbed. This absorption and transparency allows the fusing agent toabsorb enough radiation to fuse the build material in contact therewithwhile causing the 3D part to be white or slightly colored.

As used herein, the terms “3D printed part,” “3D part,” or “part” may bea completed 3D printed part or a layer of a 3D printed part.

An example of the 3D printing method 100 is depicted in FIG. 1. As anexample, the method 100 may be used to create a slightly colored orwhite 3D part.

As shown at reference numeral 102, the method 100 includes applying apolymeric or polymeric composite build material 12. One layer 14 of thebuild material 12 has been applied.

The build material 12 may be a powder, a liquid, a paste, or a gel. Thebuild material 12 may be a polymeric material or may be a compositematerial of polymer and ceramic. Examples of polymeric build material 12include semi-crystalline thermoplastic materials with a wide processingwindow of greater than 5° C. (i.e., the temperature range between themelting point and the re-crystallization temperature. Some specificexamples of the polymeric build material 12 include polyamides (PAs)(e.g., PA 11/nylon 11, PA 12/nylon 12, PA 6/nylon 6, PA 8/nylon 8, PA9/nylon 9, PA 66/nylon 66, PA 612/nylon 612, PA 812/nylon 812, PA912/nylon 912, etc.). Other specific examples of the polymeric buildmaterial 12 include polyethylene, polyethylene terephthalate (PET), andan amorphous variation of these materials. Still other examples ofsuitable polymeric build materials 12 include polystyrene, polyacetals,polypropylene, polycarbonate, polyester, thermal polyurethanes, otherengineering plastics, and blends of any two or more of the polymerslisted herein. Core shell polymer particles of these materials may alsobe used.

Any of the previously listed polymeric build materials 12 may becombined with ceramic particles to form the composite build material 12.Examples of suitable ceramic particles include metal oxides, inorganicglasses, carbides, nitrides, and borides. Some specific examples includealumina (Al₂O₃), glass, silicon mononitride (SiN), silicon dioxide(SiO₂), zirconia (ZrO₂), titanium dioxide (TiO₂), or combinationsthereof. The amount of ceramic particles that may be combined with thepolymeric build material 12 may depend on the polymeric build material12 used, the ceramic particles used, and the 3D part 38 to be formed. Inone example, the ceramic particles may be present in an amount rangingfrom about 1 wt % to about 20 wt % based on the total wt % of the buildmaterial 12.

The build material 12 may have a melting point ranging from about 50° C.to about 400° C. As examples, the build material 12 may be a polyamidehaving a melting point of 180° C., or thermal polyurethanes having amelting point ranging from about 100° C. to about 165° C.

The build material 12 may be made up of similarly sized particles ordifferently sized particles. In the examples shown herein, the buildmaterial 12 includes similarly sized particles. The term “size”, as usedherein with regard to the build material 12, refers to the diameter of aspherical particle, or the average diameter of a non-spherical particle(i.e., the average of multiple diameters across the particle). In anexample, the average size of the particles of the build material 12ranges from 5 μm to about 100 μm.

It is to be understood that the build material 12 may include, inaddition to polymer or composite particles, a charging agent, a flowaid, or combinations thereof. Charging agent(s) may be added to suppresstribo-charging. Examples of suitable charging agent(s) include aliphaticamines (which may be ethoxylated), aliphatic amides, quaternary ammoniumsalts (e.g., behentrimonium chloride or cocamidopropyl betaine), estersof phosphoric acid, polyethylene glycolesters, or polyols. Some suitablecommercially available charging agents include HOSTASTAT® FA 38 (naturalbased ethoxylated alkylamine), HOSTASTAT® FE2 (fatty acid ester), andHOSTASTAT® HS 1 (alkane sulfonate), each of which is available fromClariant Int. Ltd.). In an example, the charging agent is added in anamount ranging from greater than 0 wt % to less than 5 wt % based uponthe total wt % of the build material 12.

Flow aid(s) may be added to improve the coating flowability of the buildmaterial 12. Flow aid(s) may be particularly beneficial when theparticles of the build material 12 are less than 25 μm in size. The flowaid improves the flowability of the build material 12 by reducing thefriction, the lateral drag, and the tribocharge buildup (by increasingthe particle conductivity). Examples of suitable flow aids includetricalcium phosphate (E341), powdered cellulose (E460(ii)), magnesiumstearate (E470b), sodium bicarbonate (E500), sodium ferrocyanide (E535),potassium ferrocyanide (E536), calcium ferrocyanide (E538), bonephosphate (E542), sodium silicate (E550), silicon dioxide (E551),calcium silicate (E552), magnesium trisilicate (E553a), talcum powder(E553b), sodium aluminosilicate (E554), potassium aluminum silicate(E555), calcium aluminosilicate (E556), bentonite (E558), aluminumsilicate (E559), stearic acid (E570), or polydimethylsiloxane (E900). Inan example, the flow aid is added in an amount ranging from greater than0 wt % to less than 5 wt % based upon the total wt % of the buildmaterial 12.

In the example shown at reference numeral 102, applying the buildmaterial includes the use of the printing system 10. The printing system10 may include a supply bed 16 (including a supply of the build material12), a delivery piston 18, a roller 20, a fabrication bed 22 (having acontact surface 23), and a fabrication piston 24. Each of these physicalelements may be operatively connected to a central processing unit (notshown) of the printing system. The central processing unit (e.g.,running computer readable instructions stored on a non-transitory,tangible computer readable storage medium) manipulates and transformsdata represented as physical (electronic) quantities within theprinter's registers and memories in order to control the physicalelements to create the 3D part 38. The data for the selective deliveryof the build material 12, the fusing agent 26, etc. may be derived froma model of the 3D part to be formed.

The delivery piston 18 and the fabrication piston 24 may be the sametype of piston, but are programmed to move in opposite directions. In anexample, when a layer of the 3D part 38 is to be formed, the deliverypiston 18 may be programmed to push a predetermined amount of the buildmaterial 12 out of the opening in the supply bed 16 and the fabricationpiston 24 may be programmed to move in the opposite direction of thedelivery piston 18 in order to increase the depth of the fabrication bed22. The delivery piston 18 will advance enough so that when the roller20 pushes the build material 12 into the fabrication bed 22 and onto thecontact surface 23, the depth of the fabrication bed 22 is sufficient sothat a layer 14 of the build material 12 may be formed in the bed 22.The roller 20 is capable of spreading the build material 12 into thefabrication bed 22 to form the layer 14, which is relatively uniform inthickness. In an example, the thickness of the layer 14 ranges fromabout 90 μm to about 110 μm, although thinner or thicker layers may alsobe used. For example, the thickness of the layer 14 may range from about50 μm to about 200 μm.

It is to be understood that the roller 20 may be replaced by othertools, such as a blade that may be useful for spreading different typesof powders, or a combination of a roller and a blade.

As shown at reference numeral 104 in FIG. 1, the layer 14 of the buildmaterial 12 may be exposed to heating after the layer 14 is applied inthe fabrication bed 22 (and prior to selectively applying the fusingagent 26). Heating is performed to pre-heat the build material 12, andthus the heating temperature may be below the melting point of the buildmaterial 12. As such, the temperature selected will depend upon thebuild material 12 that is used. As examples, the heating temperature maybe from about 5° C. to about 50° C. below the melting point of the buildmaterial 12. In an example, the heating temperature ranges from about50° C. to about 350° C. In another example, the heating temperatureranges from about 150° C. to about 170° C.

Pre-heating the layer 14 of the build material 12 may be accomplishedusing any suitable heat source that exposes all of the build material 12in the fabrication bed 22 to the heat. Examples of the heat sourceinclude a thermal heat source (e.g., a heater (not shown) of thefabrication bed 22) or an electromagnetic radiation source (e.g.,infrared (IR), microwave, etc.).

After the build material 12 is applied at reference numeral 102 and/orafter the build material 12 is pre-heated at reference numeral 104, thefusing agent 26 is selectively applied on at least a portion 30 of thebuild material 12, in the layer 14, as shown at reference number 106.

As illustrated in FIG. 1 at reference numeral 106, the fusing agent 26may be dispensed from an inkjet applicator, such as an inkjet printhead28. While a single printhead is shown in FIG. 1 at reference numeral106, it is to be understood that multiple printheads may be used thatspan the width of the fabrication bed 22. The printhead 28 may beattached to a moving XY stage or a translational carriage (neither ofwhich is shown) that moves the printhead 28 adjacent to the fabricationbed 22 in order to deposit the fusing agent 26 in desirable area(s) 30.

The printhead 28 may be programmed to receive commands from the centralprocessing unit and to deposit the fusing agent 26 according to apattern of a cross-section for the layer of the 3D object that is to beformed. As used herein, the cross-section of the layer of the object tobe formed refers to the cross-section that is parallel to the contactsurface 23. In the example shown in FIG. 1 at reference numeral 106, theprinthead 28 selectively applies the fusing agent 26 on those portion(s)30 of the layer 14 that are to be fused to become the first layer of the3D part 38. As an example, if the first layer is to be shaped like acube or cylinder, the fusing agent 26 will be deposited in a squarepattern or a circular pattern (from a top view), respectively, on atleast a portion of the layer 14 of the build material 12. In the exampleshown in FIG. 1 at reference numeral 106, the fusing agent 26 isdeposited in a square pattern on the portion 30 of the layer 14 and noton the portions 32.

The fusing agent 26 includes a plasmonic resonance absorber. Theplasmonic resonance absorber allows the fusing agent 26 to absorbradiation at wavelengths ranging from 800 nm to 4000 nm, which enablesthe fusing agent 26 to convert enough radiation to thermal energy sothat the build material 12 fuses. The plasmonic resonance absorber alsoallows the fusing agent 26 to have transparency at wavelengths rangingfrom 400 nm to 780 nm, which enables the 3D part 38 to be white orslightly colored.

The absorption of the plasmonic resonance absorber is the result of theplasmonic resonance effects. Electrons associated with the atoms of theplasmonic resonance absorber may be collectively excited byelectromagnetic radiation, which results in collective oscillation ofthe electrons. The wavelengths required to excite and oscillate theseelectrons collectively are dependent on the number of electrons presentin the plasmonic resonance absorber particles, which in turn isdependent on the size of the plasmonic resonance absorber particles. Theamount of energy required to collectively oscillate the particle'selectrons is low enough that very small particles (e.g., 1-100 nm) mayabsorb electromagnetic radiation with wavelengths several times (e.g.,from 8 to 800 or more times) the size of the particles. The use of theseparticles allows the fusing agent 26 to be inkjet jettable as well aselectromagnetically selective (e.g., having absorption at wavelengthsranging from 800 nm to 4000 nm and transparency at wavelengths rangingfrom 400 nm to 780 nm).

In an example, the plasmonic resonance absorber has an average particlediameter ranging from greater than 0 nm to less than 220 nm. In anotherexample the plasmonic resonance absorber has an average particlediameter ranging from greater than 0 nm to 120 nm. In a still anotherexample, the plasmonic resonance absorber has an average particlediameter ranging from about 10 nm to about 200 nm.

In an example, the plasmonic resonance absorber is an inorganic pigment.Examples of suitable inorganic pigments include lanthanum hexaboride(LaB₆), tungsten bronzes (A_(x)WO₃), indium tin oxide (In₂O₃:SnO₂, ITO),aluminum zinc oxide (AZO), ruthenium oxide (RuO₂), silver (Ag), gold(Au), platinum (Pt), iron pyroxenes (A_(x)Fe_(y)Si₂O₆ wherein A is Ca orMg, x=1.5-1.9, and y=0.1-0.5), modified iron phosphates(A_(x)Fe_(y)PO₄), and modified copper pyrophosphates (A_(x)Cu_(y)P₂O₇).Tungsten bronzes may be alkali doped tungsten oxides. Examples ofsuitable alkali dopants (i.e., A in A_(x)WO₃) may be cesium, sodium,potassium, or rubidium. In an example, the alkali doped tungsten oxidemay be doped in an amount ranging from greater than 0 mol % to about0.33 mol % based on the total mol % of the alkali doped tungsten oxide.Suitable modified iron phosphates (A_(x)Fe_(y)PO₄) may include copperiron phosphate (A=Cu, x=0.1-0.5, and y=0.5-0.9), magnesium ironphosphate (A=Mg, x=0.1-0.5, and y=0.5-0.9), and zinc iron phosphate(A=Zn, x=0.1-0.5, and y=0.5-0.9). For the modified iron phosphates, itis to be understood that the number of phosphates may change based onthe charge balance with the cations. Suitable modified copperpyrophosphates (A_(x)Cu_(y)P₂O₇) include iron copper pyrophosphate(A=Fe, x=0-2, and y=0-2), magnesium copper pyrophosphate (A=Mg, x=0-2,and y=0-2), and zinc copper pyrophosphate (A=Zn, x=0-2, and y=0-2).Combinations of the inorganic pigments may also be used.

The amount of the plasmonic resonance absorber that is present in thefusing agent 26 ranges from about 1.0 wt % to about 20.0 wt % based onthe total wt % of the fusing agent 26. In some examples, the amount ofthe plasmonic resonance absorber present in the fusing agent 26 rangesfrom about 1.0 wt % up to about 10.0 wt %. In other examples, the amountof the plasmonic resonance absorber present in the fusing agent 26ranges from greater than 4.0 wt % up to about 15.0 wt %. It is believedthat these plasmonic resonance absorber loadings provide a balancebetween the fusing agent 26 having jetting reliability andelectromagnetic radiation absorbance efficiency.

As used herein, “vehicle” may refer to the liquid fluid in which theplasmonic resonance absorber is placed to form the fusing agent 26. Awide variety of vehicles, including aqueous and non-aqueous vehicles,may be used with the plasmonic resonance absorber. In some instances,the vehicle includes water alone or a non-aqueous solvent (e.g. dimethylsulfoxide (DMSO), ethanol, etc.) alone. In other instances, the vehiclemay further include a dispersing additive, a surfactant, a co-solvent, abiocide, an anti-kogation agent, a silane coupling agent, a chelatingagent, and combinations thereof.

When the vehicle is water-based, the aqueous nature of the fusing agent26 enables the fusing agent 26 to penetrate, at least partially, intothe layer 14 of the build material 12. The build material 12 may behydrophobic, and the presence of the co-solvent, the surfactant, and/orthe dispersing additive in the fusing agent 26 when the fusing agent 26is water-based or non-aqueous based may assist in obtaining a particularwetting behavior.

The plasmonic resonance absorber in the fusing agent 26 may, in someinstances, be dispersed with a dispersing additive. As such, thedispersing additive helps to uniformly distribute the plasmonicresonance absorber throughout the fusing agent 26. As mentioned above,the dispersing additive may also aid in the wetting of the fusing agent26 onto the build material 12. Some examples of the dispersing additiveinclude a water soluble acrylic acid polymer (e.g., CARBOSPERSE® K7028available from Lubrizol), a styrene-acrylic pigment dispersion resin(e.g., JONCRYL® 671 available from BASF Corp.), a high molecular weightblock copolymer with pigment affinic groups (e.g., DISPERBYK®-190available BYK Additives and Instruments), and combinations thereof.Whether a single dispersing additive is used or a combination ofdispersing additives is used, the total amount of dispersing additive(s)in the fusing agent 26 may range from about 10 wt % to about 200 wt %based on the wt % of the plasmonic resonance absorber in the fusingagent 26.

Surfactant(s) may also be used in the vehicle to improve the wettingproperties of the fusing agent 26. Examples of suitable surfactantsinclude a self-emulsifiable, nonionic wetting agent based on acetylenicdiol chemistry (e.g., SURFYNOL® SEF from Air Products and Chemicals,Inc.), a nonionic fluorosurfactant (e.g., CAPSTONE® fluorosurfactantsfrom DuPont, previously known as ZONYL FSO), and combinations thereof.In other examples, the surfactant is an ethoxylated low-foam wettingagent (e.g., SURFYNOL® 440 or SURFYNOL® CT-111 from Air Products andChemical Inc.) or an ethoxylated wetting agent and molecular defoamer(e.g., SURFYNOL® 420 from Air Products and Chemical Inc.). Still othersuitable surfactants include non-ionic wetting agents and moleculardefoamers (e.g., SURFYNOL® 104E from Air Products and Chemical Inc.) orwater-soluble, non-ionic surfactants (e.g., TERGITOL™ TMN-6 from The DowChemical Company). In some examples, it may be desirable to utilize asurfactant having a hydrophilic-lipophilic balance (HLB) less than 10.

Whether a single surfactant is used or a combination of surfactants isused, the total amount of surfactant(s) in the fusing agent 26 may rangefrom about 0.1 wt % to about 3 wt % based on the total wt % of thefusing agent 26.

Some examples of the co-solvent that may be added include1-(2-hydroxyethyl)-2-pyrollidinone, 2-Pyrrolidinone, 1,5-Pentanediol,Triethylene glycol, Tetraethylene glycol, 2-methyl-1,3-propanediol,1,6-Hexanediol, Tripropylene glycol methyl ether, N-methylpyrrolidone,Ethoxylated Glycerol-1 (LEG-1), and combinations thereof. Whether asingle co-solvent is used or a combination of co-solvents is used, thetotal amount of co-solvent(s) in the fusing agent 26 may range fromabout 10 wt % to about 80 wt % with respect to the total wt % of thefusing agent 26.

A biocide or antimicrobial may be added to the fusing agent 26. Examplesof suitable biocides include an aqueous solution of1,2-benzisothiazolin-3-one (e.g., PROXEL® GXL from Arch Chemicals,Inc.), quaternary ammonium compounds (e.g., BARDAC® 2250 and 2280,BARQUAT® 50-65B, and CARBOQUAT® 250-T, all from Lonza Ltd. Corp.), andan aqueous solution of methylisothiazolone (e.g., KORDEK® MLX from TheDow Chemical Co.). Whether a single biocide is used or a combination ofbiocides is used, the total amount of biocide(s) in the fusing agent 26may range from about 0.1 wt % to about 1 wt % with respect to the totalwt % of the fusing agent 26.

An anti-kogation agent may be included in the fusing agent 26. Kogationrefers to the deposit of dried ink (e.g., fusing agent 26) on a heatingelement of a thermal inkjet printhead. Anti-kogation agent(s) is/areincluded to assist in preventing the buildup of kogation. Examples ofsuitable anti-kogation agents include oleth-3-phosphate (e.g.,commercially available as CRODAFOS™ 03A or CRODAFOS™ N-3 acid fromCroda), or a combination of oleth-3-phosphate and a low molecular weight(e.g., <5,000) polyacrylic acid polymer (e.g., commercially available asCARBOSPERSE™ K-7028 Polyacrylate from Lubrizol). Whether a singleanti-kogation agent is used or a combination of anti-kogation agents isused, the total amount of anti-kogation agent(s) in the fusing agent 26may range from about 0.1 wt % to about 0.2 wt % based on the total wt %of the fusing agent 26.

A silane coupling agent may be added to the fusing agent 26 to help bondthe organic and inorganic materials. Examples of suitable silanecoupling agents include the SILQUEST® A series manufactured byMomentive.

Whether a single silane coupling agent is used or a combination ofsilane coupling agents is used, the total amount of silane couplingagent(s) in the fusing agent 26 may range from about 0.1 wt % to about50 wt % based on the wt % of the plasmonic resonance absorber in thefusing agent 26. In an example, the total amount of silane couplingagent(s) in the fusing agent 26 ranges from about 1 wt % to about 30 wt% based on the wt % of the plasmonic resonance absorber. In anotherexample, the total amount of silane coupling agent(s) in the fusingagent 26 ranges from about 2.5 wt % to about 25 wt % based on the wt %of the plasmonic resonance absorber.

The fusing agent 26 may also include other additives, such as achelating agent. Examples of suitable chelating agents include disodiumethylenediaminetetraacetic acid (EDTA-Na) and methylglycinediacetic acid(e.g., TRILON® M from BASF Corp.). Whether a single chelating agent isused or a combination of chelating agents is used, the total amount ofchelating agent(s) in the fusing agent 26 may range from 0 wt % to about1 wt % based on the total wt % of the fusing agent 26.

The fusing agent 26 may also include a colorant in addition to theplasmonic resonance absorber. While the plasmonic resonance absorberprimarily functions as an electromagnetic radiation absorber, theadditional colorant may impart color to the fusing agent and theresulting 3D part 38. The amount of the colorant that may be present inthe fusing agent 26 ranges from about 1 wt % to about 10 wt % ofpigment(s) based on the total wt % of the fusing agent 26. The colorantmay be a pigment and/or dye having any suitable color. Examples of thecolors include cyan, magenta, yellow, etc. Examples of colorants includedyes, such as Acid Yellow 23 (AY 23), Acid Yellow 17 (AY 17), Acid Red52 (AR 52), Acid Red 289 (AR 289), Reactive Red 180 (RR 180), DirectBlue 199 (DB 199), or pigments, such as Pigment Blue 15:3 (PB 15:3),Pigment Red 122 (PR 122), Pigment Yellow 155 (PY 155), and PigmentYellow 74 (PY 74).

Some examples of the fusing agent 26 that include colorant are shown inTable 1 below.

TABLE 1 Cyan Magenta Yellow Fusing Fusing Fusing Agent agent agentIngredient Specific component (wt %) (wt %) (wt %) Co-solvent2-pyrrolidone 20.00 20.00 20.00 Anti-Kogation CRODAFOS ® O3A 0.50 0.500.50 agent Surfactant SURFYNOL ® SEF 0.75 0.75 0.75 CAPSTONE ® FS-350.05 0.05 0.05 Dispersing CARBOSPERSE ® K 0.01 0.01 0.01 additive 7028Chelating TRILON ® M 0.04 0.04 0.04 agent Biocide PROXEL ® GXL 0.18 0.180.18 KORDEK ® MLX 0.14 0.14 0.14 Plasmonic Cesium tungsten oxide 25 2525 resonance stock dispersion absorber Colorant PB 15:3 2 0 0 PR 122 0 40 PY 74 0 0 2 Water Balance Balance Balance

While not shown in FIG. 1, the method 100 may further include preparingthe fusing agent 26. In one example, the fusing agent 26 may be preparedby adding the plasmonic resonance absorber to a millbase to form amixture. The millbase may include water, the silane coupling agent(e.g., SILQUEST® A manufactured by Momentive, etc.), citric acid, aco-solvent (e.g., 2-pyrrolidone), a wetting agent (e.g., isopropylalcohol), or a combination thereof. The mixture may be milled to reducethe average particle diameter of the plasmonic resonance absorber toless than 220 nm, and to form a dispersion. Any suitable millingtechnique may be used. In an example, an Ultra-Apex Bead Mill (Kotobuki)may be used with 50 μm zirconia beads. The rotor speed of the Ultra-ApexBead Mill may range from about 8 m/s to about 10 m/s. In anotherexample, a laboratory shaker may be used with 650 μm zirconium beads. Instill another example, a Fritsch mill may be used with 200 μm zirconiabeads. The rotor speed of the Fritsch mill may be 400 rotations perminute. In any of these examples, the mixture may be milled for about 1hour to about 10 hours. Alternatively, in any of the above examples, themixture may be alternated between being milled for about 1 minute toabout 3 minutes and resting for about 3 minutes to about 10 minutes forabout 100 repetitions to about 140 repetitions. The dispersion may becollect from the beads by adding water to obtain from about 5 wt % toabout 10 wt % of non-volatile solids (NVS) (based on the total wt % ofthe dispersion). In an example, the amount of the plasmonic resonanceabsorber may be from about 3 wt % to about 5 wt % of the total wt % ofthe dispersion. The dispersion may then be incorporated into the aqueousor non-aqueous vehicle to form the fusing agent 26. When a colorant isincluded in the fusing agent 26, it may be milled with the plasmonicresonance absorber, or it may be added to the aqueous or non-aqueousvehicle.

In another example, the fusing agent 26 may be prepared by firstextracting or removing the plasmonic resonance absorber from anotherdispersion. This process may involve diluting the dispersion andcentrifuging the diluted dispersion to separate the plasmonic resonanceabsorber from other dispersion components. The plasmonic resonanceabsorber may then be milled and added to the aqueous or non-aqueousvehicle to form the fusing agent 26. When a colorant is included in thefusing agent 26, it may be milled with the plasmonic resonance absorber,or it may be added to the aqueous or non-aqueous vehicle.

In still another example, the fusing agent 26 may be prepared bydiluting a tungsten bronze dispersion (such as a cesium tungsten oxidedispersion) with 2-pyrrolidone at 1:1 w/w to form a diluted dispersion.In one example, the cesium tungsten oxide dispersion, prior to dilution,may contain about 25 wt % cesium tungsten oxide and 75 wt % solvent(e.g., butyl acetate, 2-methoxy-1-methylethyl acetate, dipropyleneglycol monomethyl ether (DPM), etc.) (based on the total wt % of thecesium tungsten oxide dispersion). The diluted dispersion may bedistilled at a temperature of about 60° C. and a pressure of about 20 mmHg to form a stock dispersion including the plasmonic resonanceabsorber. The stock dispersion may then be incorporated into the aqueousor non-aqueous vehicle to form the fusing agent 26. When included, thecolorant may be added to the aqueous or non-aqueous vehicle. In anexample, the fusing agent 26 includes from about 25 wt % to about 50 wt% of the stock dispersion including the plasmonic resonance absorber(based on the total wt % of the fusing agent 26).

It is to be understood that a single fusing agent 26 may be selectivelyapplied to form the layer of the 3D part 38, or multiple fusing agents26 may be selectively applied to form the layer of the 3D part 38.

After the fusing agent 26 is selectively applied in the desiredportion(s) 30, the entire layer 14 of the build material 12 (includingthe fusing agent 26 applied to at least a portion thereof) is exposed toelectromagnetic radiation 36. This is shown at reference numeral 108 ofFIG. 1.

The electromagnetic radiation 36 is emitted from a radiation source 34,such as an IR or near-IR curing lamp, IR or near-IR light emittingdiodes (LED), a magnetron that emits microwaves, or lasers with thedesirable electromagnetic wavelengths. As an example, the radiationsource 34 is a near-infrared light source with wavelengths ranging fromabout 800 nm to about 2 μm.

In an example, the electromagnetic radiation 36 may include wavelengthsranging from about 100 nm (UV) to about 10 μm. In yet another example,the light source electromagnetic wavelengths range from about 400 nm toabout 3 μm or 4 μm (which includes near-infrared and mid-infraredradiation). As an example, the electromagnetic radiation 36 is blackbodyradiation with a maximum intensity at a wavelength of about 1100 nm.

Any radiation source 34 may be used that emits electromagneticradiation. The radiation source 34 may be attached, for example, to acarriage that also holds the inkjet printhead(s) 28. The carriage maymove the radiation source 34 into a position that is adjacent to thefabrication bed 22. The radiation source 34 may be programmed to receivecommands from the central processing unit and to expose the layer 14,including the fusing agent 26 and build material 12, to electromagneticradiation 36.

The length of time the radiation 36 is applied for, or energy exposuretime, may be dependent, for example, on one or more of: characteristicsof the radiation source 34; characteristics of the build material 12;and/or characteristics of the fusing agent 26.

The fusing agent 26 enhances the absorption of the radiation 36,converts the absorbed radiation to thermal energy, and promotes thetransfer of the thermal heat to the build material 12 in contacttherewith (i.e., in the portion 30). In an example, the fusing agent 26sufficiently elevates the temperature of the build material 12 above themelting point(s), allowing curing (e.g., sintering, binding, fusing,etc.) of the build material particles 12 in contact with the fusingagent 26 to take place. In an example, the temperature is elevated about50° C. above the melting temperature of the build material 12. Thefusing agent 26 may also cause, for example, heating of the buildmaterial 12, below its melting point but to a temperature suitable tocause softening and bonding. It is to be understood that portions 32 ofthe build material 12 that do not have the fusing agent 26 appliedthereto do not absorb enough energy to fuse. Exposure to radiation 36forms the 3D layer or part 38, as shown at reference numeral 108 in FIG.1.

While the 3D part 38 is shown as a single layer, it is to be understoodthat the 3D part 38 may include several layers. Each additional layer ofthe 3D part 38 may be formed by repeating reference numerals 102-108.For example, to form an additional layer of the 3D part 38, anadditional layer of the build material 12 may be applied to the 3D part38 shown in reference numeral 108 and the additional layer may bepreheated, may have the fusing agent 26 selectively applied thereto, andmay be exposed to radiation 36 to form that additional layer. Any numberof additional layers may be formed. When the 3D object 38 is complete,it may be removed from the fabrication bed 22, and any uncured buildmaterial 12 may be washed and then reused.

Referring now to FIG. 2, another example of the printing system 10′ isdepicted. The system 10′ includes a central processing unit 46 thatcontrols the general operation of the additive printing system 10′. Asan example, the central processing unit 46 may be a microprocessor-basedcontroller that is coupled to a memory 50, for example via acommunications bus (not shown). The memory 50 stores the computerreadable instructions 48. The central processing unit 46 may execute theinstructions 48, and thus may control operation of the system 10′ inaccordance with the instructions 48. For example, the instructions maycause the controller to utilize a build material distributor 56 todispense the build material 12, and to utilize fusing agent distributor28 (e.g., an inkjet applicator 28) to selectively dispense the fusingagent 26 to form a three-dimensional part.

In this example, the printing system 10′ includes a fusing agentdistributor 28 to selectively deliver fusing agent 26 to portion(s) 30of the layer (not shown in this figure) of build material 12 provided ona support member 58.

The central processing unit 46 controls the selective delivery of thefusing agent 26 to the layer of the build material 12 in accordance withdelivery control data 52.

In the example shown in FIG. 2, it is to be understood that thedistributor 28 is a printhead(s), such as a thermal printhead(s) or apiezoelectric inkjet printhead(s). The printhead(s) 28 may be adrop-on-demand printhead(s) or a continuous drop printhead(s).

The printhead(s) 28 may be used to selectively deliver the fusing agent26, when in the form of a suitable fluid. As described above, the fusingagent 26 includes an aqueous or non-aqueous vehicle, such as water,co-solvent(s), surfactant(s), etc., to enable it to be delivered via theprinthead(s) 28.

In one example the printhead(s) 28 may be selected to deliver drops ofthe fusing agent 26 at a resolution ranging from about 300 dots per inch(DPI) to about 1200 DPI. In other examples, the printhead(s) 28 may beselected to be able to deliver drops of the fusing agent 26 at a higheror lower resolution. The drop velocity may range from about 5 m/s toabout 24 m/s and the firing frequency may range from about 1 kHz toabout 100 kHz.

The printhead(s) 28 may include an array of nozzles through which theprinthead(s) 28 is able to selectively eject drops of fluid. In oneexample, each drop may be in the order of about 10 pico liters (pl) perdrop, although it is contemplated that a higher or lower drop size maybe used. In some examples, printhead(s) 28 is able to deliver variablesize drops.

The printhead(s) 28 may be an integral part of the printing system 10′,or it may be user replaceable. When the printhead(s) 28 is userreplaceable, they may be removably insertable into a suitabledistributor receiver or interface module (not shown).

As shown in FIG. 2, the distributor 28 may have a length that enables itto span the whole width of the support member 58 in a page-wide arrayconfiguration. In an example, the page-wide array configuration isachieved through a suitable arrangement of multiple printheads. Inanother example, the page-wide array configuration is achieved through asingle printhead with an array of nozzles having a length to enable themto span the width of the support member 58. In other examples of theprinting system 10′, the distributor 28 may have a shorter length thatdoes not enable it to span the whole width of the support member 58.

While not shown in FIG. 2, it is to be understood that the distributor28 may be mounted on a moveable carriage to enable it to movebi-directionally across the length of the support member 58 along theillustrated y-axis. This enables selective delivery of the fusing agent26 across the whole width and length of the support member 58 in asingle pass. In other examples, the distributor 28 may be fixed whilethe support member 58 is configured to move relative thereto.

As used herein, the term ‘width’ generally denotes the shortestdimension in the plane parallel to the X and Y axes shown in FIG. 2, andthe term ‘length’ denotes the longest dimension in this plane. However,it is to be understood that in other examples the term ‘width’ may beinterchangeable with the term ‘length’. As an example, the distributor28 may have a length that enables it to span the whole length of thesupport member 58 while the moveable carriage may move bi-directionallyacross the width of the support member 58.

In examples in which the distributor 28 has a shorter length that doesnot enable it to span the whole width of the support member 58, thedistributor 28 may also be movable bi-directionally across the width ofthe support member 58 in the illustrated X axis. This configurationenables selective delivery of the fusing agent 26 across the whole widthand length of the support member 58 using multiple passes.

The distributor 28 may include therein a supply of the fusing agent 26or may be operatively connected to a separate supply of the fusing agent26.

As shown in FIG. 2, the printing system 10′ also includes a buildmaterial distributor 56. This distributor 56 is used to provide thelayer (e.g., layer 14) of the build material 12 on the support member58. Suitable build material distributors 56 may include, for example, awiper blade, a roller, or combinations thereof.

The build material 12 may be supplied to the build material distributor56 from a hopper or other suitable delivery system. In the exampleshown, the build material distributor 56 moves across the length (Yaxis) of the support member 58 to deposit a layer of the build material12. As previously described, a first layer of build material 12 will bedeposited on the support member 58, whereas subsequent layers of thebuild material 12 will be deposited on a previously deposited (andsolidified) layer (e.g., layer 38).

It is to be further understood that the support member 58 may also bemoveable along the Z axis. In an example, the support member 58 is movedin the Z direction such that as new layers of build material 12 aredeposited, a predetermined gap is maintained between the surface of themost recently formed layer and the lower surface of the distributor 28.In other examples, however, the support member 58 may be fixed along theZ axis and the distributor 28 may be movable along the Z axis.

Similar to the system 10 (shown in FIG. 1), the system 10′ also includesthe radiation source 34 to apply energy to the deposited layer of buildmaterial 12 and the fusing agent 26 to cause the solidification ofportion(s) 30 of the build material 12. Any of the previously describedradiation sources 34 may be used. In an example, the radiation source 34is a single energy source that is able to uniformly apply energy to thedeposited materials, and in another example, radiation source 34includes an array of energy sources to uniformly apply energy to thedeposited materials.

In the examples disclosed herein, the radiation source 34 is configuredto apply energy in a substantially uniform manner to the whole surfaceof the deposited build material 12. This type of radiation source 34 maybe referred to as an unfocused energy source. Exposing the entire layerto energy simultaneously may help increase the speed at which athree-dimensional object may be generated.

While not shown, it is to be understood that the radiation source 34 maybe mounted on the moveable carriage or may be in a fixed position.

The central processing unit 46 may control the radiation source 34. Theamount of energy applied may be in accordance with delivery control data52.

The system 10′ may also include a pre-heater 60 that is used to pre-heatthe deposited build material 12 (as shown and described in reference toFIG. 1 at reference numeral 104). The use of the pre-heater 60 may helpreduce the amount of energy that has to be applied by the radiationsource 34.

To further illustrate the present disclosure, examples are given herein.It is to be understood that these examples are provided for illustrativepurposes and are not to be construed as limiting the scope of thepresent disclosure.

EXAMPLES Example 1

Three examples of the plasmonic resonance absorber were prepared. Theplasmonic resonance absorber used in the examples was lanthanumhexaboride (LaB₆). The samples of lanthanum hexaboride were manufacturedby Aldrich or SkySpring Nanosystems. Each example of the plasmonicresonance absorber was added to a millbase and milled to reduce itsparticle size. The general formulations of the millbase composition usedfor each mill are shown in Table 2, with the wt % of each component thatwas used.

TABLE 2 Mill 1 Mill 2 Mill 3 Ingredient Specific component (wt %) (wt %)(wt %) Plasmonic Lanthanum hexaboride 5 0 14 resonance (Aldrich)absorber Lanthanum hexaboride 0 2.5 0 (SkySpring Nanosystems) Lanthanumhexaboride 0 0 0 (Colorflex) Co-solvent 2-pyrrolidone 0 0 20 WettingIsopropyl alcohol 0 0 2 agent Silane SILQUEST ® A 40 20 0 coupling agentDispersing JONCRYL ® 671 0 0 6 Additive Additive Citric acid 8 5 0 WaterBalance Balance Balance

The lanthanum hexaboride used in mill 1 had an initial average particlesize of about 1 μm. The slurry formed of the lanthanum hexaboride andthe millbase used in mill 1 had a pH of 8.0. The slurry of mill 1 wasmilled in an Ultra-Apex Bead Mill (UAM-015 manufactured by Kotobuki)with 50 μm zirconia beads at a rotor speed of about 8 m/s to about 10m/s for 5 hours. The particle size of the lanthanum hexaboride aftermilling was 127 nm.

The lanthanum hexaboride used in mill 2 had an initial average particlesize of about 1 μm. The slurry formed of the lanthanum hexaboride andthe millbase used in mill 2 had a pH of 8.5. The slurry of mill 2 wasmilled in an Ultra-Apex Bead Mill (UAM-015 manufactured by Kotobuki)with 50 μm zirconia beads at a rotor speed of about 8 m/s to about 10m/s for 2 hours. The particle size of the lanthanum hexaboride aftermilling was 8 nm.

The lanthanum hexaboride used in mill 3 had an initial average particlesize of about 1 μm. The slurry formed of the lanthanum hexaboride andthe millbase used in mill 3 was milled with a laboratory shaker with 650μm zirconium beads for 9 hours. The particle size of the lanthanumhexaboride after milling was 210 nm.

This example illustrates that various forms of lanthanum hexaboride canbe processed to obtain a particle size suitable for inkjet printing, andfor use in a fusing agent.

Example 2

Three examples of the fusing agent were prepared. The plasmonicresonance absorber used in the example fusing agent compositions waseither cesium tungsten oxide (in a stock dispersion) or lanthanumhexaboride (LaB₆). The general formulations of the example fusing agentcompositions are shown in Table 3, with the wt % of each component thatwas used.

TABLE 3 Fusing Fusing Fusing agent agent agent Ingredient Specificcomponent 1 (wt %) 2 (wt %) 3 (wt %) Co-solvent 2-pyrrolidone 20.0020.00 20.00 Isopropyl alcohol 0 0 0.16 Anti-Kogation CRODAFOS ® O3A 0.500.50 0.50 agent Surfactant SURFYNOL ® SEF 0.75 0.75 0.75 CAPSTONE ®FS-35 0.05 0.05 0.05 Dispersing CARBOSPERSE ® K 0.01 0.01 0.01 additive7028 JONCRYL ® 671 0 0 0.48 Chelating TRILON ® M 0.04 0.04 0.04 agentBiocide PROXEL ® GXL 0.18 0.18 0.18 KORDEK ® MLX 0.14 0.14 0.14 Silanecoupling SILQUEST ® A 0 0 0.28 agent Plasmonic Cesium tungsten oxide 5025 0 resonance stock dispersion absorber Lanthanum 0 0 1.12 hexaboride(Aldrich) Water Balance Balance Balance

The cesium tungsten oxide stock dispersion used in fusing agents 1 and 2was prepared using a commercially available, cesium tungsten oxidedispersion, namely YMS-01A-2 (manufactured by Sumitomo Metals Co.). Thegeneral formulation of YMS-01A-2 as described by the manufacturer in theMaterial Safety Data Sheet is shown in Table 4, with the wt % of eachcomponent.

TABLE 4 cesium tungsten oxide dispersion-YMS-01A-2 Ingredient Specificcomponent wt % Solvent butyl acetate 1.7 2-methoxy-1-methylethyl acetate58.9 dipropylene glycol monomethyl 1.9 ether (DPM) cesium tungsten oxide25 Others Information not available 12.5

The YMS-01A-2 cesium tungsten oxide dispersion was diluted with2-pyrrolidone at 1:1 w/w. The diluted dispersion was distilled at atemperature of 60° C. and a pressure of 20 mm Hg. The resultingdispersion was a deep blue, non-opaque fluid, containing 25 wt % ofsolids (based on the total wt % of the dispersion), and was used as thecesium tungsten oxide stock dispersion in fusing agents 1 and 2.

Fusing agents 1 and 2 were prepared by mixing together all of the fusingagent components except for the cesium tungsten oxide stock dispersion(i.e., 2-pyrrolidone, CRODAFOS® 03A, SURFYNOL® SEF, CAPSTONE® FS-35,CARBOSPERSE® K 7028, TRILON® M, PROXEL® GXL, KORDEK® MLX, and water).The mixture was put on a magnetic stirrer, and the cesium tungsten oxidestock dispersion was added drop-wise under constant mixing. Theresulting cesium tungsten oxide fusing agents (i.e., fusing agents 1 and2) were light blue, slightly opaque fluids.

The lanthanum hexaboride used in fusing agent 3 was generated by mill 3from example 1. Except for the components in the dispersed solution thatresulted from mill 3, all of the other fusing agent components forfusing agent 3 (i.e., 18.4 wt % 2-pyrrolidone, CRODAFOS® 03A, SURFYNOL®SEF, CAPSTONE® FS-35, CARBOSPERSE® K 7028, TRILON® M, PROXEL® GXL,KORDEK® MLX, and 71.93 wt % water (based on the total wt % of the fusingagent)) were mixed together and put on a stirrer bar. The dispersedsolution that resulted from mill 3 (i.e., lanthanum hexaboride(Aldrich), JONCRYL® 671, isopropyl alcohol, 1.6 wt % 2-pyrrolidone, and4.64 wt % water (based on the total wt % of the fusing agent)) was addeddrop-wise under constant mixing. The resulting lanthanum hexaboridefusing agent (i.e., fusing agent 3) was a green, slightly opaque fluid.

This example illustrates that various fusing agents can be formulatedusing examples of the plasmonic resonance absorber disclosed herein.

Example 3

Two examples and one comparative example of tensile testing specimens(“dog bones”) were printed. The build material used to print the exampleand comparative dog bones was polyamide-12 (PA-12). The fusing agentused to print the example dog bones was either fusing agent 1 fromexample 2 or fusing agent 3 from example 2. The fusing agent used toprint the comparative dog bones was a carbon black-based fusing agent.The carbon-black based fusing agent had a formulation similar to theblack ink in an HP 88 printhead.

For each example and comparative dog bone, the fusing agent was thermalinkjet printed with a HP761 printhead (manufactured by Hewlett-PackardCompany) in a pattern on a portion of the PA-12 in subsequent layers.Each layer was about 100 μm in thickness. New layers were spread ontothe fabrication bed from a supply region using a roller. The temperatureof the supply region was set at 130° C. The temperature of the printingregion was set at 160° C. with a platen underneath it heated to 165° C.The example and comparative dog bones were printed at an ink density of1.25 drops per pixel at 600 dpi resolution. The example and comparativedog bones were then exposed to high-intensity light from two sets of two500 watt halogen bulbs passing over the fabrication bed. After thefusing agent was applied, the fabrication bed experienced three lampexposures per layer. After all layers were printed, the example andcomparative dog bones were removed from the fabrication bed andsandblasted to remove excess powder.

For comparative example 1, 12 dog bones were printed (labeled CLB_#,CRF_#, CRB_#, CLF_#, where the # corresponds with the fuse speed used).The speed at which the halogen bulbs passed over the fabrication bed(i.e., fuse speed) was either 20 inches per second (ips), 23 ips, or 28ips. The density was measured for each dog bone printed with the carbonblack-based fusing agent. The results of the density measurements areshown below in Table 5.

TABLE 5 Fuse Density speed (% Specimen (ips) theoretical) CLB_20 20 96.7CRF_20 20 98.3 CRB_20 20 97.2 CLF_20 20 100.6 CRF_23 23 91.1 CLF_23 2393.9 CLB_23 23 92.2 CRB_23 23 96.1 CRF_28 28 86.7 CLF_28 28 88.9 CLB_2828 88.3 CRB_28 28 89.4

For the examples printed with fusing agent 1, seven dog bones wereprinted (labeled LB_#, RF_#, RB_#, LF_#, where the # corresponds withthe fuse speed used). The fuse speed was either 20 ips or 16 ips. Thestrength, percent (%) elongation, Young's Modulus, and mass weremeasured for each dog bone printed with fusing agent 1. These tensiletests were carried out on an INSTRON® tensile testing machine. Theresults of these measurements are shown below in Table 6.

TABLE 6 Fuse % Young's speed Strength Elongation Modulus Mass DensitySpecimen (ips) (MPa) (%) (MPa) (g) (% theoretical) LB_20 20 39.83 32.081266 1.75 97.2 RF_20 20 37.61 22.41 1093 1.68 93.3 RB_20 20 38.03 24.661097 1.66 92.2 LF_20 20 39.39 37.37 1071 1.74 96.7 RF_16 16 37.99 42.981076 1.91 106 LF_16 16 38.27 44.50 1183 1.95 108 LB_16 16 39.21 35.321162 1.98 110

The masses obtained for the dog bones printed with fusing agent 1 werewithin 10% (+/−) of the theoretical (fully fused) mass of 1.8 g forcesium tungsten oxide fused parts. The dog bones produced with fusingagent 1 at 20 ips are very close in density to the black dog bonesproduced with the carbon black-based fusing agent at the same fusespeed. Obtaining such high densities with fusing agent 1 was unexpectedbecause the optical density of fusing agent 1 is substantially lowerthan than the optical density of the carbon black-based fusing agent(see below). An overall comparison of the masses of the dog bonesprinted with fusing agent 1 and the dog bones printed with the carbonblack-based fusing agent indicates that a slower fusing speed helps toobtain higher density.

The elongation of the dog bones printed with fusing agent 1 wasexcellent compared to the typical elongation (i.e., 14%) of the dogbones printed with the carbon black-based fusing agent. The strength andYoung's Modulus of the dog bones printed with fusing agent 1 were withinan acceptable range (i.e., ≥36 MPa and ≥900 MPa, respectively) and wereonly slightly lower than the typical strength (i.e., ˜43 MPa) andYoung's Modulus (i.e., 1650 MPa) of the dog bones printed with thecarbon black-based fusing agent. The increase in the elastic and/orplastic behavior (as demonstrated by elongation measurement) andacceptable strength and Young's Modulus measurements demonstrate thatfusing agent 1 works well as a fusing agent.

These results indicate that a cesium tungsten oxide-based fusing agentcan function well as a fusing agent to print parts with acceptable fusespeed, strength, percent (%) elongation, Young's Modulus, and mass.

For the examples printed with fusing agent 3, four dog bones wereprinted. The fuse speed was 16 ips. The mass was measured for each dogbone printed with fusing agent 3. The results of these measurements areshown below in Table 7.

TABLE 7 Fuse speed Mass Specimen (ips) (g) RF 16 0.72 LF 16 0.77 RB 160.80 LB 16 0.80

The masses obtained for the dog bones printed with fusing agent 3 were39% of the theoretical (fully fused) mass of 1.8 g for lanthanumhexaboride fused parts. The low mass of the dog bones printed withfusing agent 3 may be due, at least in part, to the lower amount ofplasmonic absorber in fusing agent 3.

These results indicate that a lanthanum hexaboride-based fusing agentcan function as a fusing agent to print solid parts. The mass of partsformed with fusing agent 3 may be increased by incorporating more of theplasmonic absorber in the fusing agent.

The optical density of fusing agent 1, fusing agent 3, and the carbonblack-based fusing agent was measured using an X-rite eXact™densitometer. The results of the optical density measurements are shownbelow in Table 8.

TABLE 8 Fusing agent Optical density Fusing agent 1 0.59 ± 0.2 (cesiumtungsten oxide) Fusing agent 3 0.21 ± 0.02 (lanthanum hexaboride) Carbonblack-based 0.92 ± 0.1 fusing agent

As shown in Table 8, the optical density of fusing agent 1 is 0.31 lessthan the carbon black-based fusing agent. The dog bones printed withfusing agent 1 had a light bluish hue. A black and white photographicimage of specimens RB_20, LB_20, LF_20, and RF_20 (from right to left)printed with fusing agent 1 is shown in FIG. 3. Also shown in Table 8 isthat the optical density of fusing agent 3 is 0.71 less than the opticaldensity of the carbon black-based fusing agent. The dog bones printedwith fusing agent 3 had a light greenish hue. A black and whitephotographic image of specimens RB, LB, LF, and RF (from right to left)printed with fusing agent 3 is shown in FIG. 4. These results indicatethat either a cesium tungsten oxide-based fusing agent or a lanthanumhexaboride-based fusing agent can be used to print parts with loweroptical density and/or a lighter hue (e.g., than parts printed with acarbon black-based fusing agent).

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range from about 50° C. to about 350° C. should beinterpreted to include not only the explicitly recited limits of about50° C. to about 350° C., but also to include individual values, such as57° C., 95° C., 225° C., 300° C., etc., and sub-ranges, such as fromabout 70° C. to about 325° C., from about 60° C. to about 170° C., etc.Furthermore, when “about” is utilized to describe a value, this is meantto encompass minor variations (up to +/−10%) from the stated value.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting.

What is claimed is:
 1. A three-dimensional (3D) printing method,comprising: applying a polymeric or polymeric composite build material;selectively applying a fusing agent on at least a portion of thepolymeric or polymeric composite build material, the fusing agentincluding: an aqueous or non-aqueous vehicle; and an inorganic pigmentdispersed in the aqueous or non-aqueous vehicle, wherein the inorganicpigment is selected from the group consisting of lanthanum hexaboride,tungsten bronzes, indium tin oxide, aluminum zinc oxide, rutheniumoxide, silver, gold, platinum, iron pyroxenes, modified iron phosphates(A_(x)Fe_(y)PO₄), modified copper pyrophosphates (A_(x)Cu_(y)P₂O₇), andcombinations thereof; and exposing the polymeric or polymeric compositebuild material to electromagnetic radiation, thereby fusing the portionof the polymeric or polymeric composite build material in contact withthe fusing agent to form a layer.
 2. The method as defined in claim 1wherein the fusing agent includes the aqueous vehicle, and wherein theaqueous vehicle includes water, a co-solvent, an anti-kogation agent, asurfactant, a dispersing additive, a chelating agent, and a biocide. 3.The method as defined in claim 2 wherein the fusing agent includes fromabout 25 wt % to about 50 wt % of a stock dispersion including theinorganic pigment.
 4. The method as defined in claim 2 wherein theaqueous vehicle further includes a silane coupling agent.
 5. The methodas defined in claim 4 wherein the fusing agent includes from about 1 wt% to about 10 wt % of the inorganic pigment.
 6. The method as defined inclaim 4 wherein the fusing agent includes from greater than 4.0 wt % toabout 10 wt % of the inorganic pigment.
 7. The method as defined inclaim 1, further comprising incorporating a colorant into the aqueous ornon-aqueous vehicle.
 8. The method as defined in claim 1 wherein priorto selectively applying the fusing agent, the method further comprisesheating the polymeric or polymeric composite build material to atemperature ranging from about 50° C. to about 350° C.
 9. The method asdefined in claim 1 wherein the selectively applying the fusing agent isaccomplished with an inkjet applicator.
 10. The method as defined inclaim 1, further comprising repeating the applying, selectivelyapplying, and exposing to form a 3D part, wherein the 3D part is white.11. A three-dimensional (3D) printing system, comprising: a supply ofpolymeric or polymeric composite build material; a build materialdistributor; a supply of a fusing agent, the fusing agent including: anaqueous or non-aqueous vehicle; and an inorganic pigment dispersed inthe aqueous or non-aqueous vehicle, wherein the inorganic pigment isselected from the group consisting of lanthanum hexaboride, tungstenbronzes, indium tin oxide, aluminum zinc oxide, ruthenium oxide, silver,gold, platinum, iron pyroxenes, modified iron phosphates(A_(x)Fe_(y)PO₄), modified copper pyrophosphates (A_(x)Cu_(y)P₂O₇), andcombinations thereof; an inkjet applicator for selectively dispensingthe fusing agent; a controller; and a non-transitory computer readablemedium having stored thereon computer executable instructions to causethe controller to: utilize the build material distributor to dispensethe build material; and utilize the inkjet applicator to selectivelydispense the fusing agent to form a three-dimensional part.
 12. The 3Dprinting system as defined in claim 11 wherein the aqueous vehicleincludes: a co-solvent present in an amount ranging from about 10 wt %to about 80 wt % based on a total wt % of the fusing agent; ananti-kogation agent present in an amount ranging from about 0.1 wt % toabout 2 wt % based on the total wt % of the fusing agent; a surfactantpresent in an amount ranging from about 0.1 wt % to about 3 wt % basedon the total wt % of the fusing agent; a dispersing additive present inan amount ranging from about 10 wt % to about 200 wt % of the inorganicpigment; a chelating agent present in an amount ranging from 0 wt % toabout 1 wt % based on the total wt % of the fusing agent; a biocidepresent in an amount ranging from about 0.1 wt % to about 1 wt % basedon the total wt % of the fusing agent; a silane coupling agent presentin an amount ranging from about 0.1 wt % to about 50 wt % of theinorganic pigment; and a balance of water.
 13. The 3D printing system asdefined in claim 12 wherein the fusing agent includes from about 1 wt %to about 10 wt % of the inorganic pigment.
 14. The 3D printing system asdefined in claim 11 wherein the aqueous vehicle includes: a co-solventpresent in an amount ranging from about 10 wt % to about 80 wt % basedon a total wt % of the fusing agent; an anti-kogation agent present inan amount ranging from about 0.1 wt % to about 2 wt % based on the totalwt % of the fusing agent; a surfactant present in an amount ranging fromabout 0.1 wt % to about 3 wt % based on the total wt % of the fusingagent; a dispersing additive present in an amount ranging from about 10wt % to about 200 wt % of the inorganic pigment; a chelating agentpresent in an amount ranging from 0 wt % to about 1 wt % based on thetotal wt % of the fusing agent; a biocide present in an amount rangingfrom about 0.1 wt % to about 1 wt % based on the total wt % of thefusing agent; and a balance of water.
 15. The 3D printing system asdefined in claim 14 wherein the fusing agent includes from about 25 wt %to about 50 wt % of a stock dispersion including the inorganic pigment.16. The 3D printing system as defined in claim 11 wherein the fusingagent further includes a colorant.